The effects of electrolyte concentration in the emulsion polymerization of styrene (original) (raw)
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The effect of vinyl benzyl chloride on emulsion polymerization of styrene
Polystyrene latexes were prepared, in the presence of, vinyl benzyl chloride (VBC) monomer. These particles were synthesized in surfactant-free batch radical emulsion polymerization of styrene and VBC monomer mixture, with 2,2'azobis(2-amidino propane)di-hydrochloride (V50) initiator. The polymerization kinetics was found to be rapid, as a function of VBC monomer concentration in the polymerization recipe. It is interesting to notice that high VBC amount leads to marked coagulum formation. The final hydrodynamic particle size was found to be slightly sensitive to the VBC concentration in the investigated range. The presence of VBC at the surface of the particles was investigated by XPS analysis. Unauthenticated Download Date | 3/6/15 12:35 PM
Journal of Polymer Science Part A-polymer Chemistry, 2005
The emulsion polymerization of styrene above the critical micelle concentration has been experimentally studied from a low final polymer content up to a high polymer content (∼50%). A maximum in the molecular weight (M) evolution has been observed in all cases. The presence or absence of such a maximum depends on the relative values of the rate of free-radical entry (ρ) and the rate of chain transfer to the monomer (KtrCMp, where Ktr is the chain transfer to monomer rate coefficient and CMp is the monomer concentration in particles). If ρ ≪ KtrCMp, M is constant and equal to Kp/Ktr (where Kp is the propagation rate coefficient), except at very low particles sizes typical of the early stages of the reaction, in which the chain length is limited by the particle size. On the other hand, if ρ ≫ KtrCMp, M is determined by both CMp and ρ. It is proposed that ρ is determined by the sum of the entry of the oligomeric radicals formed in the aqueous phase and those contained in particles that undergo limited coagulation. This coagulative entry can become very significant; therefore, reactor hydrodynamics can play a major role in the kinetic behavior observed. Disagreement between Clay and Gilbert's model and molecular weight distribution data can be ascribed, to a lesser or greater extent, to the degree of correctness of the quasi-steady-state and instantaneous-termination approaches. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1963–1972, 2005
Emulsion polymerization of styrene: Nucleation studies with nonionic emulsifier
1982
The nucleation mechanism of styrene emulsion polymerization in the presence of the nonionic surfactant Emulphogene BC-840 was investigated. It was found that the conversion-time curves of this system show two rate regions. The change in rate occurs at ca. 40% conversion. Second-stage nucleation leads to a faster rate and consequently to a bimodally dispersed latex. The particle size distribution is relatively narrow before 40% conversion. The bimodally dispersed latex shows a bimodal molecular weight distribution in gel permeation chromatography and the results from fractional "creaming" of the latex indicate that the small-size particles contain the higher-molecular-weight polymer.
Microemulsion polymerization of styrene
Journal of Polymer Science Part A: Polymer Chemistry, 1989
Initiation of polymerization in styrene oil-in-water microemulsions by water-soluble potassium persulfate or oil-soluble 2,2'-azobis-(2-methyl butyronitrile) at 70°C gave stable latexes which were bluish and less translucent than the original microemulsions. The effects of initiator concentration, polymerization temperature, and monomer concentration on the kinetics, particle size distributions, and molecular weight distributions were investigated. The kinetics of polymerization were measured by dilatometry. In all cases, the polymerization rate shows only two intervals, which increased to a maximum and then decreased. There was no apparent constant rate period and no gel effect. A longer nucleation period was found for polymerizations initiated by potassium persulfate as compared to 2,2'-azobis-(2-rnethyl butyronitrile). The small latex particle size (20-30 nm) and high polymer molecular weight (1-2 X lo6) implies that each latex particle consists of two or three polystyrene molecules. The maximum polymerization rate and number of particles varied with the 0.47 and 0.40 powers of potassium persulfate concentration, and the 0.39 and 0.38 powers of 2,2'-azobis-(2-rnethyl butyronitrile) concentration, respectively. This is consistent with the 0.4 power predicted by Smith-Ewart Case 2 kinetics. Microemulsion polymerizations of styrene-toluene mixtures at the same oil-water phase ratio gave lower polymerization rates and lower molecular weights, but the same latex particle size as with styrene alone. A mechanism is proposed, which comprised initiation and polymerization in the microemulsion droplets, by comparing the kinetics of microemulsion polymerization with conventional emulsion and miniemulsion polymerization systems.
Emulsion Polymerization of Styrene and Vinyl Acetate with Cationic Surfactant
Macromolecular Symposia, 2007
In this study, the emulsion homopolymerization system containing vinyl acetate and styrene, potassium persulfate, and a new cationic surfactant was studied in the classical glass emulsion polymerization reactor. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate and styrene latex properties were investigated depending on surfactant percentage in homopolymerizations.
The role of acid-base equilibrium in emulsifier-free styrene polymerization with a carboxyl-containing initiator, namely, 4,4'-azobis(4-cyanovaieric acid) (CVA), was investigated at the pH of the starting emulsion from 8.3 to 11.5. It was found that the polymerization kinetics, the particle diameter, and the degree of polydispersity of the latexes synthesized at different CVA concentrations and styrene/water ratios depend substantially on both the initial pH of the reaction mixture and the pattern of the changes in pH during the synthesis. Both minima and maxima are observed in the kinetic dependences of pH in different periods of synthesis. The deviations of pH from the starting values were as large as two pH units. The influence of the buffer salt (NaJB'O,) concentration on the polymerization process and the parameters of the latexes synthesized was also studied. It was shown that the establishment of the acid-base equilibrium in the system depends also on the formation of the surface-active oligomers and their distribution between the emulsion phases. The results obtained indicate that the surface charge formed upon ionization of the end carboxyl groups of polymer chains is the main factor of stabilization of growing polymer particles in the system studied.
Acrylo-Styrene Latex. I. Influence of the Emulsifier Amount and Distribution on Product Properties
Polymer-Plastics Technology and Engineering, 2001
Emulsifiers play an important part in obtaining emulsion acrylostyrene resins. They influence the polymer particle formation, the process development rate, and the final system stability in time and toward electrolytes as well. The emulsifiers affect the characteristics of the coating system based on this type of resin due to their indirect influence on resin properties. Finally, they can be found in the formed film. There is an optimum combination of emulsifiers that correspond to every application of mixture of monomers. The present article is of a study of the influence of the emulsifier amount and distribution on an acrylo-styrene resin in paints with good washability, long-term stability, and optimum rheology.
Journal of Polymer Science Part A: Polymer Chemistry, 2000
A detailed mathematical model of the kinetics of styrene emulsion polymerization has been proposed. Its main features/assumptions are compartmentalization, micellar and homogeneous nucleation, particle formation by both initiator-derived and desorbed radicals, dependence on the particle size of the rate coefficients, thermodynamic considerations, and aqueous phase kinetics. The model predicts that micellar nucleation dominates over homogeneous nucleation and that the evolution of the nucleation rate reaches a maximum, where desorbed radicals have an important contribution. Initiator-derived radicals with only one monomeric unit have also a significant contribution on the rate of capture in particles. The results suggest that the correctness of the instantaneous termination approach depends not only on the size of the particle, but also on the type of entering radical (initiator-derived or monomeric).